Effects Of Cold Shock Combined With Salicylic Acid Treatment On Reducing Chilling Injury Of Cucumber Fruit And The Possible Mechanisms

Cucumber fruit is popular among consumers for its crispy,sweet,juicy and rich nutrition.Cold storage is one of the most widely used preservation technologies for postharvest cucumber.However,as the typical cold-sensitive fruit,cucumber is susceptible to chilling injury below 7?10?.Symptoms include surface pitting,dark watery patches,which limit application of cold chain technology in postharvest preservation of cucumber.In addition,cucumber fruit has extremely high water content and thin skin,which is likely to cause water loss,wilting.thus accelerated the decay and deterioration.Therefore,the sensory quality and commercial value of cucumber fruit will be reduced.To investigate the mechanisms of cold shock combined with salicylic acid treatment on chilling injury of cucumber fruit,the effects of cold shock(CST)?salicylic acid(SA)and the combination of cold shock and salicylic acid(CST+SA)treatments on energy metabolism,oxygen metabolism,proline metabolism and polyamine metabolism in cucumber fruit("tuoni" 102)stored at low temperature were studied,respectively.This study provides a theoretical basis for alleviation of cucumber fruit.The main results were as follows:1.The best SA and CST treatments conditions were screened out by the chilling injury index mainly,and cucumber fruit were treated with SA,CST and CST+SA under the optimal conditions.The effects of these three treatments on chilling injury and quality of refrigerated cucumber fruit were studied.The results indicated that the treatments of SA,CST and CST+SA effectively alleviated the chilling injury,inhibited the relative electric conductivity and the increase of malondialdehyde content of cucumber fruit.Besides,these three treatments also inhibited the reduction of chlorophyll,ascorbic acid,soluble protein content and firmness,and maintained the quality of cucumber fruit during storage.And among these three treatments,the effect of CST+SA treatment was the best.2.The effects of SA,CST and CST+SA treatments on reactive oxygen metabolism and energy metabolism in cucumber fruit stored at low temperature were studied.Compared with SA and CST treatments,CST+SA treatment significantly increased the scavenging ability of DPPH free radicals and hydroxyl free radicals,inhibited the accumulation of O2·-and H2O2 content in cucumber fruit during cold storage.The activities of enzymes involved in oxygen metabolism including SOD,CAT,APX,POD were also enhanced significantly.Thus,maintained the balance of reactive oxygen metabolism in cucumber,improve its postharvest cold resistance;In addition,these three treatments markedly retarded the decline of ATP and ADP content,inhibited the increase of AMP content and maintained higher energy charge compared with control.The activities of enzymes involved in energy metabolism including H+-ATPase,Ca2+-ATPase,SDH and CCO were also enhanced significantly.3.The effects of SA,CST and CST+SA treatments on proline metabolism and polyamine metabolism in cucumber fruit stored at low temperature were studied.The results demonstrated that these three treatments improved P5CS and OAT activities and inhibited PDH activity,which played an important role in the accumulation of proline of cucumber fruit.And among these three treatments,the effect of CST+SA treatment was the best.The results also indicated that the activities of enzymes involved in polyamine metabolism including ADC,ODC,PAO and DAO were also enhanced significantly.Thus,the integrity of the cell membrane was maintained,and the cold resistance of cucumber fruit during cold storage was improved.As a result,the occurrence of chilling injury of cucumber fruit was delayed.And among these three treatments,the effect of CST+SA treatment was the best.